JP2005294314A - Multilayer ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer ceramic capacitor 1 in which enhancement in TC bias characteristics can be expected while having various electric characteristics, especially a sufficient dielectric constant, even when an interlayer dielectric layer 2 is made thin. <P>SOLUTION: The multilayer ceramic capacitor 1 consists of an internal electrode layer 3, and an interlayer dielectric layer 2 having a thickness of less than 2 μm wherein the interlayer dielectric layer 2 contains a plurality of dielectric particles 2a. Assuming the standard deviation of particle size distribution of entire dielectric particles 2a in the interlayer dielectric layer 2 is σ (no unit), the mean particle diameter of entire dielectric particles 2a in the interlayer dielectric layer 2 is D50 (unit: μm), and the ratio of dielectric particles (rough particles) having mean particle diameter of 2.25 times or more of D50 existing in the entire dielectric particles 2a is p (unit: %), the σ and p satisfy following relation of σ<0.130, p<12%. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a multilayer ceramic capacitor.

  The multilayer ceramic capacitor includes an element body having a structure in which a plurality of dielectric layers and internal electrode layers are alternately stacked, and a pair of external terminal electrodes formed at both ends of the element body. In this multilayer ceramic capacitor, first, a pre-firing dielectric layer and a pre-firing internal electrode layer are alternately laminated in a necessary number to produce a pre-firing element body, and then, after firing this, the post-firing element body It is manufactured by forming a pair of external terminal electrodes at both ends.

  In the production of the multilayer ceramic capacitor, since the pre-firing dielectric layer and the pre-firing internal electrode layer are fired simultaneously, the conductive material contained in the pre-firing internal electrode layer includes a dielectric material contained in the pre-firing dielectric layer. It is required to have a melting point higher than the sintering temperature of the powder, not to react with the dielectric raw material powder, and not to diffuse into the dielectric layer after firing.

  In recent years, in order to satisfy these requirements, the conductive material contained in the internal electrode layer before firing is replaced with a noble metal such as Pt or Pd that has been conventionally used, and the sintering temperature of the dielectric material powder is lowered. Developed by using an Ag-Pd alloy as the conductive material contained in the internal electrode layer before firing, or using an inexpensive base metal such as Ni that can be fired in a reducing atmosphere by imparting reduction resistance to the dielectric material. Has been.

  The case where Ni is used for the conductive material contained in the internal electrode layer before firing is illustrated. Ni has a lower melting point than the dielectric raw material powder contained in the pre-firing dielectric layer. Therefore, when the pre-fired dielectric layer and the pre-fired internal electrode layer containing Ni as the conductive material are fired simultaneously, the firing of the dielectric raw material powder is caused by the difference in the sintering start temperature between the dielectric raw material powder and Ni. The Ni internal electrode becomes thicker as the crystallization progresses and eventually tends to be interrupted. Therefore, there is a technique for adding a dielectric material for addition as a sintering inhibitor to the internal electrode layer paste for forming the internal electrode layer for the purpose of suppressing discontinuity and sintering suppression due to this kind of firing. It has been proposed (see Patent Documents 1 to 5). This additive dielectric material has the property of diffusing from the internal electrode layer side to the interlayer dielectric layer side during simultaneous firing of the pre-fired interlayer dielectric layer and the pre-fired internal electrode layer.

  By the way, in recent years, with the miniaturization of various electronic devices, it has been required to realize a reduction in size / capacity, a reduction in price, and a high reliability of a multilayer ceramic capacitor mounted inside the electronic device. In order to meet such a demand, the thickness of the fired internal electrode layer and the fired interlayer dielectric layer disposed between the opposed fired internal electrode layers has been reduced. Specifically, the fired thickness per layer of the interlayer dielectric layer after firing has been reduced to about 1 μm, and accordingly, the thickness before firing per layer of the interlayer dielectric layer before firing is also reduced. Layered.

  As the pre-firing interlayer dielectric layer is thinned, the content of the dielectric material per dielectric layer for forming it is reduced.

  For example, an internal electrode layer paste in which a dielectric material for addition is added at a predetermined weight ratio with respect to Ni as a conductive material is prepared, and the paste is made into a plurality of layers whose thickness before firing is gradually reduced. Consider a case where the pre-firing interlayer dielectric layer is applied and formed with a predetermined thickness. At this time, the weight ratio of the content of the dielectric material for addition in the internal electrode layer to the content of the dielectric material in the interlayer dielectric layer before firing (content of the dielectric material for addition in the internal electrode layer / firing) The content of the dielectric material in the previous interlayer dielectric layer) increases stepwise as the thickness of the pre-fired interlayer dielectric layer on which the internal electrode layer paste is applied and formed decreases. Become. This is because as the thickness of the interlayer dielectric layer before firing becomes thinner, the content of the dielectric material in the interlayer dielectric layer before firing decreases, and the denominator of the above weight ratio formula becomes smaller. As a result, the value of the weight ratio increases.

  This means that, when considered from the side of the interlayer dielectric layer before firing, the thinner the thickness, the relatively larger the amount of dielectric material for addition diffused from the internal electrode layer side. . That is, the relative diffusion amount from the internal electrode layer side to the interlayer dielectric layer side increases.

  In addition, along with the thinning of the interlayer dielectric layer before firing described above, the internal electrode layer before firing is also required to be thinned. In order to thin the internal electrode layer before firing, this is formed. In addition to the conductive material such as Ni in the internal electrode layer paste to be made, miniaturization of the dielectric material for addition is required.

  However, if the additive dielectric material diffusing from the internal electrode layer side to the interlayer dielectric layer side is miniaturized during firing, it promotes the grain growth of the dielectric particles constituting the interlayer dielectric layer. May affect the microstructure of the interlayer dielectric layer. As described above, the more the diffusion amount of the dielectric material for addition from the internal electrode layer side to the interlayer dielectric layer side increases, the more so. When the thickness of the interlayer dielectric layer after firing was 2.0 μm or more, the influence on the microstructure could be ignored, but when the thickness of the interlayer dielectric layer after firing was reduced to less than 2.0 μm , The influence on the fine structure tends to increase. Due to the influence of such a fine structure, various characteristics such as bias characteristics and reliability of the obtained multilayer ceramic capacitor may be deteriorated.

  As a solution to these various problems, Patent Document 6 discloses an average particle size of dielectric particles that are not in contact with dielectric particles that are in contact with the internal electrode layer after firing by adjusting the additive composition to the internal electrode layer paste. Techniques for adjusting the diameter ratio, additive component concentration ratio, and core-shell ratio have been proposed. According to the technique described in Patent Document 6, the dielectric layer can be thinned without deteriorating temperature characteristics, tan δ, and lifetime. However, in the technique described in Patent Document 6, the improvement of the bias characteristics is not sufficient and still has a problem.

Patent Document 7 discloses a multilayer ceramic capacitor characterized in that the average particle size of dielectric particles in the vicinity of the external electrode is the same as or smaller than the average particle size of dielectric particles in the effective region.
However, the technique described in Patent Document 7 is intended to prevent cracks during sintering of the external electrode, and improvement in bias characteristics cannot be expected.
JP-A-5-62855 JP 2000-277369 A JP 2001-307939 A JP 2003-77761 A Japanese Patent Application Laid-Open No. 2003-100544 JP 2003-1224049 A JP 2003-133164 A

  An object of the present invention is to provide a multilayer ceramic capacitor that can be expected to improve various electric characteristics, in particular, a TC bias characteristic while having a sufficient dielectric constant even when an interlayer dielectric layer is thinned.

In order to achieve the above object, according to the present invention,
A multilayer ceramic capacitor having an internal electrode layer and a dielectric layer having a thickness of less than 2 μm,
The dielectric layer includes a plurality of dielectric particles,
Provided is a multilayer ceramic capacitor in which σ satisfies σ <0.130, where σ (no unit) is the standard deviation of the particle size distribution of the entire dielectric particles in the dielectric layer.

  Preferably, when the average particle diameter of the entire dielectric particles in the dielectric layer is D50 (unit: μm), dielectric particles (coarse particles) having an average particle diameter of 2.25 times or more of D50 ) Is defined as p (unit:%), and the p satisfies p <12%.

The multilayer ceramic capacitor according to the present invention can be manufactured, for example, by the following method. However, the manufacturing method of the multilayer ceramic capacitor of the present invention is not limited to the following method.
In the following method, the dielectric layer is composed of barium titanate (particularly, the composition ratio (BaO) _{0.990 to 1 in} which the molar ratio m of the so-called A site and B site is m = 0.990 to 1.035) _. It illustrates a case including a main component composed of barium titanate) represented by _.035 · TiO _2.

The method is
Firing a laminate formed using a dielectric layer paste containing a dielectric material and an internal electrode layer paste containing a dielectric material for addition,
The dielectric material in the dielectric layer paste includes a main component material and a subcomponent material,
The main component material is represented by a composition formula (BaO) _m · TiO ₂ , and the molar ratio m in the formula is barium titanate having m = 0.990 to 1.035,
The dielectric material for addition in the internal electrode layer paste includes at least a main component material for addition,
The main component material for addition is barium titanate represented by a composition formula (BaO) _{m ′} · TiO ₂ , wherein the molar ratio m ′ in the formula is 0.993 <m ′ <1.050. A method for manufacturing a multilayer ceramic capacitor.

In this method, the so-called A / B of the main component raw material for addition contained in the dielectric material for addition in the internal electrode layer paste, that is, the A site (the part of “(BaO)” in the above formula), and the B site The molar ratio m ′ with (the “TiO ₂ ” portion in the above formula) is adjusted. Thereby, the presence state of the dielectric particles constituting the dielectric layer after firing can be easily controlled.

The composition of the dielectric oxide constituting the main component is not limited to the barium titanate represented by the above-described composition formula (BaO) _{0.990 to 1.035} · TiO _2. The following dielectric oxide can be applied. The dielectric oxide is represented by a composition formula (AO) _m · BO ₂ , in which the symbol A is at least one element selected from Sr, Ca and Ba, and the symbol B is at least Ti and Zr. It is one element, and the molar ratio m is m = 0.990-1.035.

  Preferably, the additive main component material has an ignition loss of less than 10.00%. By controlling the ignition loss of the main ingredient for addition together with the molar ratio m ′ of the main ingredient for addition, the presence state of the dielectric particles constituting the dielectric layer after firing is more suitably controlled. Can do.

  In this method, the additive dielectric material only needs to contain “at least the main component material for addition”, and may further contain the subcomponent material for addition. In this case, the subcomponent raw material for addition may be the same as or different from the composition of the subcomponent raw material contained in the dielectric raw material in the dielectric layer paste.

  The material constituting the internal electrode layer of the multilayer ceramic capacitor is not particularly limited in the present invention, and a noble metal can be used in addition to the base metal. When the internal electrode layer is made of a base metal, the dielectric layer includes Mn, Cr, Si, Ca, Ba, Mg, V, W, Ta, Nb, and R (R) in addition to the main component such as barium titanate. May contain subcomponents including one or more kinds of oxides of one or more rare earth elements such as Y) and compounds that become these oxides upon firing. By containing an auxiliary component, even if baked in a reducing atmosphere, it is not made into a semiconductor, and the characteristics as a capacitor can be maintained. Thus, when manufacturing a multilayer ceramic capacitor having a dielectric layer containing subcomponents in addition to the main component, the dielectric material contained in the dielectric layer paste contains the main component and subcomponents after firing. Contains the main component raw material and subcomponent raw material to be formed. In this case, as described above, the additive dielectric material contained in the internal electrode layer paste contains the additive subcomponent material in addition to the additive main component material.

Preferably, the dielectric layer contains barium titanate represented by a composition formula (BaO) _m · TiO ₂ as a main component, wherein the molar ratio m is m = 0.990 to 1.035. It contains magnesium oxide and rare earth element oxide as components, and is further selected from at least one selected from barium oxide and calcium oxide as another subcomponent, and from silicon oxide, manganese oxide, vanadium oxide, and molybdenum oxide. Containing at least one species.

At this time, the dielectric material for addition contained in the internal electrode layer paste is represented by the composition formula (BaO) _{m ′} · TiO ₂ as the main component material for addition, and the molar ratio m ′ in the formula is 0.993. <M ′ <1.050 barium titanate, magnesium oxide (including a compound that becomes magnesium oxide after firing) and rare earth element oxide as additive subcomponent materials for addition, and other subcomponents And at least one selected from barium oxide (including a compound that becomes barium oxide after firing) and calcium oxide (including a compound that becomes calcium oxide after firing), silicon oxide, manganese oxide (a compound that becomes manganese oxide after firing) And at least one selected from vanadium oxide and molybdenum oxide.

  In the present invention, the dielectric layer simply expressed as “dielectric layer” means one or both of the interlayer dielectric layer and the outer dielectric layer.

  The inventors of the present invention focused on the existence state of a plurality of dielectric particles in the dielectric layer and made extensive studies. As a result, the particle size distribution of the entire dielectric particle in the dielectric layer was sharpened, and the variation in particle size. Even when the thickness of the interlayer dielectric layer is reduced to less than 2 μm by reducing the standard deviation σ of the particle size distribution of the entire dielectric particles in the dielectric layer, various electrical characteristics In particular, it has been found that the effect of improving the TC bias characteristics can be obtained while having a sufficient dielectric constant.

  By reducing the standard deviation σ, the ratio p of coarse dielectric particles (coarse particles) present in the entire dielectric particles in the interlayer dielectric layer is reduced, but preferably, as described above, p < It is desirable to satisfy 12%. Thereby, the effect of improving the TC bias characteristic is further enhanced.

  That is, according to the present invention, even when the interlayer dielectric layer is thinned, it is possible to provide a multilayer ceramic capacitor that can be expected to improve various electrical characteristics, particularly TC bias characteristics while having a sufficient dielectric constant. it can.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention, FIG. 2 is an enlarged cross-sectional view of a main part of an interlayer dielectric layer 2 shown in FIG. 1, and FIG. FIG. 4 is a SEM image showing the cross-sectional state of the sintered body after thermal etching of the sample 9 showing the example, and FIG. 5 is sintering after thermal etching of the sample 1 showing the comparative example. FIG. 6 is a graph showing the relationship between the particle size and frequency of the dielectric particles constituting the interlayer dielectric layer in the sample 9 showing the example, and FIG. 7 is in the sample 1 showing the comparative example. 3 is a graph showing the relationship between the particle size and frequency of dielectric particles constituting an interlayer dielectric layer.

  In the present embodiment, as a multilayer ceramic capacitor having an internal electrode layer and a dielectric layer, a plurality of internal electrode layers and interlayer dielectric layers are alternately stacked, and the stacking direction of these internal electrode layers and interlayer dielectric layers is A multilayer ceramic capacitor in which outer dielectric layers are disposed at both outer ends will be described as an example.

Multilayer Ceramic Capacitor As shown in FIG. 1, a multilayer ceramic capacitor 1 according to an embodiment of the present invention includes a capacitor element body 10 having a configuration in which interlayer dielectric layers 2 and internal electrode layers 3 are alternately stacked. A pair of external electrodes 4 are formed at both ends of the capacitor element body 10 so as to be electrically connected to the internal electrode layers 3 arranged alternately in the element body 10. The internal electrode layers 3 are laminated such that the side end faces are alternately exposed on the surfaces of the two opposite ends of the capacitor element body 10. The pair of external electrodes 4 are formed at both ends of the capacitor element body 10 and are connected to the exposed end surfaces of the alternately arranged internal electrode layers 3 to constitute a capacitor circuit.

  The shape of the capacitor element body 10 is not particularly limited, but is usually a rectangular parallelepiped shape. Also, there is no particular limitation on the dimensions, and it may be an appropriate dimension according to the application. Usually, however, the length (0.4 to 5.6 mm) × width (0.2 to 5.0 mm) × height It is about (0.2-1.9 mm).

  In the capacitor element body 10, outer dielectric layers 20 are disposed at both outer end portions in the stacking direction of the internal electrode layer 3 and the interlayer dielectric layer 2 to protect the inside of the element body 10.

The composition of the interlayer dielectric layer and the outer dielectric layer, the interlayer dielectric layer 2 and the outer dielectric layer 20 is not particularly limited in the present invention. For example, it is composed of the following dielectric ceramic composition.

The dielectric ceramic composition of the present embodiment contains, as a main component, barium titanate represented by a composition formula (BaO) _m · TiO ₂ and having a molar ratio m of m = 0.990 to 1.035. To do.

  The dielectric ceramic composition of the present embodiment contains subcomponents together with the main component. As subcomponents, there are oxides of Mn, Cr, Ca, Ba, Mg, V, W, Ta, Nb and R (R is one or more of rare earth elements such as Y) and compounds that become oxides by firing. What contains more than a kind is illustrated. By adding the subcomponent, the characteristics as a capacitor can be obtained even in firing in a reducing atmosphere. As impurities, trace components such as C, F, Li, Na, K, P, S, and Cl may be contained in an amount of about 0.1 wt% or less. However, in the present invention, the composition of the interlayer dielectric layer 2 and the outer dielectric layer 20 is not limited to the above.

In the present embodiment, as the interlayer dielectric layer 2 and the outer dielectric layer 20, those having the following compositions are preferably used. The composition is represented by a composition formula (BaO) _m · TiO ₂ as a main component, and contains barium titanate having a molar ratio m of m = 0.990 to 1.035, and magnesium oxide as an accessory component. And at least one selected from the group consisting of barium oxide and calcium oxide, and at least one selected from silicon oxide, manganese oxide, vanadium oxide, and molybdenum oxide. It contains. Then, barium titanate is [(BaO) _{0.990 to 1.035} · TiO ₂ ], magnesium oxide is MgO, rare earth oxide is R ₂ O ₃ , barium oxide is BaO, and calcium oxide is to CaO, silicon oxide to SiO _2, manganese oxide to MnO, vanadium oxide to _V 2 _{O 5,} when converted respectively molybdenum oxide to _{MoO 3, [(BaO) 0.990~1.035} · TiO 2 The ratio to 100 mol is MgO: 0.1 to 3 mol, R ₂ O ₃ : more than 0 mol to 5 mol or less, BaO + CaO: 0.5 to 12 mol, SiO ₂ : 0.5 to 12 mol, MnO: 0 mol More than 0.5 mol, V ₂ O ₅ : 0 to 0.3 mol, MoO ₃ : 0 to 0.3 mol.

  Various conditions such as the number of laminated layers and thickness of the interlayer dielectric layer 2 may be appropriately determined according to the purpose and application. In this embodiment, the thickness of the interlayer dielectric layer 2 is preferably less than 2 μm, more preferably The layer is thinned to 1.5 μm or less, more preferably 1 μm or less. In the present embodiment, even when the thickness of the interlayer dielectric layer 2 is reduced as described above, various electrical characteristics of the capacitor 1, particularly TC bias characteristics are improved while having a sufficient dielectric constant. The thickness of the outer dielectric layer 20 is, for example, about 30 μm to several hundred μm.

  As shown in FIG. 2, the interlayer dielectric layer 2 includes a plurality of dielectric particles 2a and a grain boundary phase formed between a plurality of adjacent dielectric particles 2a.

  The plurality of dielectric particles 2a are composed of contact dielectric particles 22a that are in contact with the internal electrode layer 3 and non-contact dielectric particles 24a that are not in contact with the internal electrode layer. The contact dielectric particle 22a is in contact with one of the pair of internal electrode layers 3 sandwiching the interlayer dielectric layer 2 including the contact dielectric particle 22a, and is in contact with both. Absent.

Here, the standard deviation of the particle size distribution of the entire dielectric particle 2a in the interlayer dielectric layer (part contributing to the capacitance) 2 is σ (no unit), and the dielectric particles in the interlayer dielectric layer 2 When the average particle diameter of 2a as a whole is D50 (unit: μm), dielectric particles (coarse particles) having an average particle diameter of 2.25 times or more of D50 are present in the entire dielectric particles 2a. Let the ratio be p (unit:%). Here, the average particle diameter D50 of the entire dielectric particle 2a means the average particle diameter of the contact dielectric particles 22a and the non-contact dielectric particles 24a. The average particle diameter is an average particle diameter that does not include dielectric particles in the outer dielectric layer 20 at a portion that does not contribute to capacitance. Note that D50 here is obtained by cutting the capacitor element body 10 in the stacking direction of the dielectric layers 2 and 20 and the internal electrode layer 3 to obtain an average area of 200 or more dielectric particles 2a in the cross section shown in FIG. It is a value obtained by measuring and calculating the diameter as an equivalent circle diameter by a factor of 1.5.
At this time, in this embodiment, σ satisfies σ <0.130. Preferably σ satisfies 0.125 or less, more preferably 0.120 or less. If the value of σ is too large, problems such as a decrease in bias characteristics and reliability occur. The lower limit of σ is preferably as small as possible.

  In the present embodiment, it is preferable that p satisfies p <12%. More preferably, 10% or less is satisfied. If the standard deviation σ is small, the ratio p is considered to be proportionally smaller. The lower limit of p is preferably as small as possible.

  The grain boundary phase usually includes an oxide of a material constituting the dielectric material or the internal electrode material, an oxide of a material added separately, or an oxide of a material mixed as an impurity during the process.

Internal Electrode Layer The internal electrode layer 3 shown in FIG. 1 is made of a base metal conductive material that substantially functions as an electrode. As the base metal used as the conductive material, Ni or Ni alloy is preferable. The Ni alloy is preferably an alloy of Ni and one or more selected from Mn, Cr, Co, Al, Ru, Rh, Ta, Re, Os, Ir, Pt and W, and the Ni content in the alloy is It is preferably 95% by weight or more. In addition, in Ni or Ni alloy, various trace components such as P, C, Nb, Fe, Cl, B, Li, Na, K, F, and S may be contained in an amount of about 0.1% by weight or less. .

  In the present embodiment, the thickness of the internal electrode layer 3 is preferably reduced to less than 2 μm, more preferably 1.5 μm or less.

External Electrode As the external electrode 4 shown in FIG. 1, at least one of Ni, Pd, Ag, Au, Cu, Pt, Rh, Ru, Ir, or an alloy thereof can be used. Usually, Cu, Cu alloy, Ni, Ni alloy, etc., Ag, Ag—Pd alloy, In—Ga alloy, etc. are used. Although the thickness of the external electrode 4 should just be determined timely according to a use, it is preferable that it is normally about 10-200 micrometers.

Method for Manufacturing Multilayer Ceramic Capacitor Next, an example of a method for manufacturing the multilayer ceramic capacitor 1 according to this embodiment will be described.

(1) First, the dielectric layer paste that will form the interlayer dielectric layer 2 and the outer dielectric layer 20 shown in FIG. 1 after firing, and the internal electrode layer 3 shown in FIG. 1 after firing. An internal electrode layer paste is prepared.
Dielectric Layer Paste A dielectric layer paste is prepared by kneading a dielectric material and an organic vehicle.

  The dielectric material includes a main component material and a subcomponent material that form the main component and subcomponents constituting the dielectric layers 2 and 20 after firing. Each of these component raw materials can be appropriately selected from various compounds to be composite oxides and oxides, such as carbonates, nitrates, hydroxides, organometallic compounds, and the like, and can be used in combination.

  The dielectric material is usually used as a powder having an average particle size of 0.4 μm or less, preferably about 0.05 to 0.30 μm. Here, the average particle diameter is a value obtained by observing the raw material grains with an SEM and converting them to equivalent circle diameters.

  The organic vehicle contains a binder and a solvent. As a binder, various usual binders, such as ethyl cellulose, polyvinyl butyral, an acrylic resin, can be used, for example. The solvent is not particularly limited, and organic solvents such as terpineol, butyl carbitol, acetone, toluene, xylene and ethanol are used.

  The dielectric layer paste can also be formed by kneading a dielectric material and a vehicle in which a water-soluble binder is dissolved in water. The water-soluble binder is not particularly limited, and polyvinyl alcohol, methyl cellulose, hydroxyethyl cellulose, water-soluble acrylic resin, emulsion and the like are used.

  The content of each component in the dielectric layer paste is not particularly limited. For example, the dielectric layer paste can be prepared so as to contain about 1 to about 50% by weight of a solvent.

  The dielectric layer paste may contain additives selected from various dispersants, plasticizers, dielectrics, subcomponent compounds, glass frit, insulators, and the like, if necessary. When these additives are added to the dielectric layer paste, the total content is desirably about 10% by weight or less.

Internal Electrode Layer Paste In this embodiment, the internal electrode layer paste is prepared by kneading a conductive material, an additive dielectric material, and an organic vehicle.

  As the conductive material, Ni, Ni alloy, or a mixture thereof is used. There are no particular restrictions on the shape of such a conductive material, such as a spherical shape or a flake shape, and a mixture of these shapes may be used. In addition, the particle diameter of the conductive material is usually a spherical one having an average particle diameter of 0.5 μm or less, preferably about 0.01 to 0.4 μm. This is because a more advanced thinning can be realized. The conductive material is preferably contained in the internal electrode layer paste in an amount of 35 to 60% by weight.

  The dielectric material for addition has an effect of suppressing the sintering of the internal electrode (conductive material) during the firing process. In this embodiment, the dielectric material for addition contains the main component material for addition and the subcomponent material for addition.

In this embodiment, the main component material for addition is represented by the composition formula (BaO) _{m ′} · TiO ₂ , and the molar ratio m ′ in the formula is 0.993 <m ′ <1.050, preferably 0.8. Barium titanate satisfying 995 ≦ m ′ ≦ 1.035, more preferably 1.000 ≦ m ′ ≦ 1.020 is used. By using barium titanate whose adjusted main component raw material m ′ is adjusted, the state of existence of the dielectric particles 2a constituting each dielectric layer 2 after firing is controlled. Various electrical characteristics, particularly TC bias characteristics are improved while having a sufficient dielectric constant. When m ′ increases, σ at the interlayer dielectric layer 2 of the obtained capacitor 1 tends to decrease. If m ′ becomes too large, there is a tendency for sintering to be insufficient.

  In the present embodiment, a material having a specific ignition loss is used as the main component material for addition. By using a main component material having a specific ignition loss as an additive, the particle structure of the interlayer dielectric layer 2 can be effectively controlled, and the bias characteristics of the capacitor 1 can be improved more efficiently. The ignition loss of the main component material for addition is less than 10.00%, preferably 8.10% or less, more preferably 5.50% or less, and particularly preferably 3.85% or less. If the ignition loss becomes excessive, the bias characteristics tend not to be improved. Note that the lower the lower limit of the ignition loss, the better. Ultimately, 0 (zero)% is ideal, but it is usually difficult to produce such a main component material for addition.

  Here, the “ignition loss” is a heat treatment of the main component raw material for addition (heating in air at a heating rate of 300 ° C./hour, from room temperature to 1200 ° C., and holding at 1200 ° C. for 10 minutes. ) And the weight change rate when held at 200 to 1200 ° C. for 10 minutes. Ignition loss is considered to be caused by the adsorption component or OH group normally contained in the dielectric material for addition being blown off by the heat treatment.

  The average particle size of the main component material for addition may be the same as the particle size of the main component material contained in the dielectric material in the dielectric layer paste, but is preferably smaller, more preferably 0.01-0. .2 μm, particularly preferably 0.01 to 0.15 μm. In addition, it is known that the value of an average particle diameter has a correlation with a specific surface area (SSA).

  The dielectric material for addition (in some cases, only the main component material for addition or in some cases includes both the main component material for addition and the subcomponent material for addition. The same applies hereinafter unless otherwise specified) However, it is preferably produced through steps such as an oxalate method, a hydrothermal synthesis method, a sol-gel method, a hydrolysis method, and an alkoxide method. By using this method, an additive dielectric material including the additive main component material having the specific ignition loss and m ′ (so-called A / B) can be efficiently produced.

  The dielectric material for addition is contained in the internal electrode layer paste in an amount of preferably 5 to 30% by weight, more preferably 10 to 20% by weight, based on the conductive material. If the content of the dielectric material for addition in the paste is too small, the effect of suppressing the sintering of the conductive material is lowered, and if too much, the continuity of the internal electrodes is lowered. That is, if the content of the dielectric material for addition is too small or too large, both can cause inconveniences such as a sufficient capacitance as a capacitor cannot be secured.

  The organic vehicle contains a binder and a solvent.

  Examples of the binder include ethyl cellulose, acrylic resin, polyvinyl butyral, polyvinyl acetal, polyvinyl alcohol, polyolefin, polyurethane, polystyrene, and copolymers thereof. The binder is preferably contained in the internal electrode layer paste in an amount of 1 to 5% by weight with respect to the mixed powder of the conductive material and the dielectric material for addition. If the amount of the binder is too small, the strength tends to decrease. If the amount is too large, the metal filling density of the electrode pattern before firing decreases, and it becomes difficult to maintain the smoothness of the internal electrode layer 3 after firing. is there.

  As the solvent, any known solvent such as terpineol, dihydroterpineol, butyl carbitol, and kerosene can be used. The solvent content is preferably about 20 to 50% by weight with respect to the entire paste.

  The internal electrode layer paste may contain a plasticizer. Examples of the plasticizer include phthalic acid esters such as benzylbutyl phthalate (BBP), adipic acid, phosphoric acid esters, glycols, and the like.

  (2) Next, a green chip is produced using the dielectric layer paste and the internal electrode layer paste. When the printing method is used, the dielectric layer paste and the internal electrode layer paste having a predetermined pattern are stacked and printed on the carrier sheet, cut into a predetermined shape, and then peeled off from the carrier sheet to obtain a green chip. When using the sheet method, a dielectric layer paste is formed on a carrier sheet with a predetermined thickness to form a green sheet, and the internal electrode layer paste is printed in a predetermined pattern on the green sheet. Laminate to make a green chip.

  (3) Next, the obtained green chip is debindered. For example, as shown in FIG. 3, the debinder increased the ambient temperature T0 from, for example, room temperature (25 ° C.) toward the debuy holding temperature T1 at a predetermined temperature increase rate, and held T1 for a predetermined time. Thereafter, the temperature is lowered at a predetermined temperature lowering rate.

  In the present embodiment, the rate of temperature rise is preferably 5 to 300 ° C./hour, more preferably 10 to 100 ° C./hour. The buy-out holding temperature T1 is preferably 200 to 400 ° C., more preferably 220 to 380 ° C., and the holding time of the T1 is preferably 0.5 to 24 hours, more preferably 2 to 20 hours. The temperature lowering rate is preferably 5 to 300 ° C./hour, more preferably 10 to 100 ° C./hour.

The treatment atmosphere of the binder removal is preferably air or a reducing atmosphere. As the atmosphere gas in the reducing atmosphere, it is preferable to use, for example, a wet mixed gas of N ₂ and H ₂ . The oxygen partial pressure in the treatment atmosphere is preferably 10 ⁻⁴⁵ to 10 ⁵ Pa. If the oxygen partial pressure is too low, the binder removal effect is reduced, and if it is too high, the internal electrode layer tends to be oxidized.

  (4) Next, the green chip is fired. For firing, as shown in FIG. 3, for example, the ambient temperature T0 is increased from room temperature (25 ° C.) toward the firing holding temperature T2, for example, at a predetermined rate of temperature rise, and the T2 is held for a predetermined time. This is a step of lowering the ambient temperature at a predetermined temperature drop rate.

  In the present embodiment, the rate of temperature rise is preferably 50 to 500 ° C./hour, more preferably 100 to 300 ° C./hour.

  The firing holding temperature T2 is preferably 1100 to 1350 ° C, more preferably 1100 to 1300 ° C, still more preferably 1150 to 1250 ° C, and the holding time of T2 is preferably 0.5 to 8 hours, more preferably 1 to 3 hours. If T2 is too low, densification is insufficient even if the holding time of T2 is lengthened, and if it is too high, capacity due to growth of dielectric particles, electrode breakage, and diffusion of a conductive material constituting the internal electrode layer. Deterioration of temperature characteristics and reduction of the dielectric ceramic composition constituting the dielectric layer are likely to occur.

The temperature lowering rate is preferably 50 to 500 ° C./hour, more preferably 150 to 300 ° C./hour. The treatment atmosphere for firing is preferably a reducing atmosphere. As the atmosphere gas in the reducing atmosphere, it is preferable to use, for example, a wet mixed gas of N ₂ and H ₂ .
The oxygen partial pressure in the firing atmosphere is preferably 6 × 10 ⁻⁹ to 10 ⁻⁴ Pa. If the oxygen partial pressure is too low, the conductive material of the internal electrode layer may be abnormally sintered and interrupted, and if it is too high, the internal electrode layer tends to oxidize.

  (5) Next, when the green chip is fired in a reducing atmosphere, it is preferable to perform a heat treatment (annealing) subsequently. Annealing is a process for re-oxidizing the dielectric layer, thereby obtaining the characteristics of the final capacitor.

  For example, as shown in FIG. 3, the annealing is performed by increasing the ambient temperature T0 from, for example, room temperature (25 ° C.) toward the annealing holding temperature T3 at a predetermined heating rate, and holding T3 for a predetermined time. This is a step of lowering the ambient temperature T0 at a predetermined temperature drop rate.

  In the present embodiment, the rate of temperature rise is preferably 100 to 300 ° C./hour, more preferably 150 to 250 ° C./hour.

  The annealing holding temperature T3 is preferably 800 to 1100 ° C., more preferably 900 to 1100 ° C., and the holding time of T3 is preferably 0 to 20 hours, more preferably 2 to 10 hours. If T3 is too low, oxidation of the dielectric layer 2 becomes insufficient, so the IR is low and the IR life tends to be short. If T3 is too high, not only will the internal electrode layer 3 oxidize and the capacity will decrease, but the internal electrode layer 3 will react with the dielectric substrate, causing deterioration in capacity-temperature characteristics, IR, and IR life. Is likely to occur.

  The temperature lowering rate is preferably 50 to 500 ° C./hour, more preferably 100 to 300 ° C./hour.

The annealing treatment atmosphere is preferably a neutral atmosphere. As the atmospheric gas in the neutral atmosphere, for example, it is preferable to use humidified N ₂ gas. In annealing, the temperature may be changed to the holding temperature T3 in an N ₂ gas atmosphere, and the atmosphere may be changed, or the entire annealing process may be a humidified N ₂ gas atmosphere. The oxygen partial pressure in the annealing atmosphere is preferably 2 × 10 ^{−4 to 1} Pa. If the oxygen partial pressure is too low, reoxidation of the dielectric layer 2 is difficult, and if it is too high, the internal electrode layer 3 tends to oxidize.

  In the present embodiment, the annealing may be composed of only a temperature raising process and a temperature lowering process. That is, the temperature holding time may be zero. In this case, the holding temperature T3 is synonymous with the maximum temperature.

In the above-described binder removal processing, firing and annealing, for example, a wetter or the like may be used to wet the N ₂ gas, mixed gas, or the like. In this case, the water temperature is preferably about 0 to 75 ° C. The binder removal, firing, and annealing may be performed continuously or may be performed separately.

  The capacitor element body 10 made of a sintered body is formed by the above processes.

  (6) Next, the external electrode 4 is formed on the obtained capacitor element body 10. The external electrode 4 is formed by polishing the end face of the capacitor element body 10 composed of the sintered body by, for example, barrel polishing or sand blasting, and then, generally, Ni, Pd, Ag, Au, Cu, It can be formed by a known method such as baking an external electrode paste containing at least one of Pt, Rh, Ru, Ir, or an alloy thereof, or applying an In—Ga alloy. If necessary, a coating layer may be formed on the surface of the external electrode 4 by plating or the like.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, in the range which does not deviate from the summary of this invention, it can implement in various aspects. . For example, in the above-described embodiment, the binder removal processing, firing, and annealing are performed independently, but the present invention is not limited to this, and at least two steps may be performed continuously. In the case of performing continuously, after removing the binder, the atmosphere is changed without cooling, the temperature is raised to the holding temperature T2 at the time of firing, firing is performed, and then the temperature is lowered to reach the annealing holding temperature T3. Sometimes it is preferable to perform annealing by changing the atmosphere.

  Hereinafter, the present invention will be described based on further detailed examples, but the present invention is not limited to these examples.

Example 1
Preparation of Dielectric Layer Paste First, a dielectric material, PVB (polyvinyl butyral) resin as a binder, DOP (dioctyl phthalate) as a plasticizer, and ethanol as a solvent were prepared.

The dielectric material is represented by barium titanate (specifically, composition formula (BaO) _m · TiO ₂ having an average particle diameter of about 0.2 μm as a main component material, and the molar ratio m in the above formula is m = 1.005 with respect to barium titanate) of, as a subcomponent material, MnCO _3: 0.2 mol%, MgO: 0.5 _{mol%, V} 2 O 5: 0.3 _{mol%, Y} 2 O ₃ : 2 mol%, CaCO ₃ : 3 mol%, BaCO ₃ : 3 mol%, SiO ₂ : 3 mol% were wet-mixed in a ball mill for 16 hours and dried.

  Next, 10% by weight of binder, 5% by weight of plasticizer, and 150% by weight of solvent are weighed with respect to the dielectric material, kneaded with a ball mill, and slurried to obtain a dielectric layer paste. Obtained.

Preparation of Internal Electrode Layer Paste Ni particles having an average particle size of 0.2 μm as a conductive material, an additive dielectric material, an ethylcellulose resin as a binder, and terpineol as a solvent were prepared.

As a dielectric material for addition, barium titanate as a main component material for addition (specifically, barium titanate represented by a composition formula (BaO) _{m ′} · TiO ₂ , that is, Ba _{m ′} TiO _{2 + m ′} ). And those containing MnCO ₃ , MgO, V ₂ O ₅ , Y ₂ O ₃ , CaCO ₃ , BaCO _3, and SiO ₂ as subcomponent materials for addition. However, with respect to barium titanate as the main ingredient material for addition, as shown in Table 1, for each sample, the one in which the molar ratio m ′ and the ignition loss in the composition formula were changed was used.

In addition, the value of the ignition loss of the main component raw material for addition in each table is determined by heating barium titanate of the main component raw material powder for addition from room temperature to 1200 ° C. at a heating rate of 300 ° C./hour in the air. This is the value of the rate of change in weight in the range of 200 ° C. to 1200 ° C. (10 minutes) in this heat treatment, held for 10 minutes at 1200 ° C. (unit:%). In Table 1, for example, “−5.00%” indicates that when the weight at 200 ° C. of heating is 100, the weight after 10 minutes at 1200 ° C. becomes 95 and decreases by 5.00%. ing. The calculation formula is shown below.
Weight change rate = ((W _after −W _before ) / W _before ) × 100.
In the formula, W _after : weight of heat treatment 1200 ° C., 10 minutes, W _before : weight at heat 200 ° C.

  Next, 20% by weight of dielectric material for addition was added to the conductive material. 5% by weight of binder and 35% by weight of solvent are weighed and added to the mixed powder of conductive material and dielectric material for addition, kneaded with a ball mill, and slurried to obtain an internal electrode layer paste. It was.

Production of Multilayer Ceramic Chip Capacitor Sample Using the obtained dielectric layer paste and internal electrode layer paste, a multilayer ceramic chip capacitor 1 shown in FIG. 1 was produced as follows.

  First, a dielectric layer paste was applied to a predetermined thickness on a PET film by a doctor blade method and dried to form a ceramic green sheet having a thickness of 2 μm. In this example, this ceramic green sheet was used as the first green sheet, and a plurality of these were prepared.

  On the obtained first green sheet, the internal electrode layer paste was formed in a predetermined pattern by screen printing to obtain a ceramic green sheet having an electrode pattern with a thickness of about 1 μm. In this example, this ceramic green sheet was used as the second green sheet, and a plurality of these were prepared.

The first green sheets were laminated to a thickness of 300 μm to form a green sheet group. Eleven second green sheets are laminated on the green sheet group, and the same green sheet group as above is further laminated and formed thereon, and heated under conditions of a temperature of 80 ° C. and a pressure of 1 ton / cm ^2. Pressurized to obtain a green laminate.

  Next, the obtained laminate was cut into a size of 3.2 mm in length, 1.6 mm in width, and 1.0 mm in height, and then subjected to binder removal treatment, firing, and annealing under the following conditions to obtain a sintered body. Obtained. A graph showing each temperature change of the binder removal processing, firing and annealing is shown in FIG.

  The binder removal was performed under the conditions of a temperature rising rate: 30 ° C./hour, a holding temperature T1: 260 ° C., a holding time: 8 hours, a temperature falling rate: 200 ° C./hour, and a processing atmosphere: an air atmosphere.

Firing is performed at a heating rate of 200 ° C./hour, a holding temperature T2: refer to the table, a holding time of 2 hours, a cooling rate of 200 ° C./hour, a processing atmosphere: a reducing atmosphere (oxygen partial pressure: 10 ⁻⁶ Pa to N The mixed gas of ₂ and H ₂ was adjusted by passing water vapor).

As for annealing, temperature rising rate: 200 ° C./hour, holding temperature T3: 1050 ° C., holding time: 2 hours, cooling rate: 200 ° C./hour, treatment atmosphere: neutral atmosphere (oxygen partial pressure: 0.1 Pa to N ₂ The gas was adjusted by passing water vapor).

  A wetter was used to wet the gas during firing and annealing, and the water temperature was 20 ° C.

  The average particle diameter (D50) of the entire dielectric particle 2a in the interlayer dielectric layer 2 was calculated as follows. The obtained sintered body was polished from the end of the internal electrode layer to half the length, and the polished surface was mirror-polished with diamond paste. Thereafter, thermal etching treatment (temperature increase rate and temperature decrease rate: 300 ° C./hour, holding temperature: 1200 ° C., holding time: 10 minutes) was performed, and the particles were observed with a scanning electron microscope (SEM). And the cross-sectional area (S) of particle | grains was calculated | required from the SEM image which shows the cross-sectional state of the sintered compact after a thermal etching. However, the observation target position was in a range of 100 μm × 100 μm including the center of the polished surface, and any five views (observing about 90 contact dielectric particles per view) were selected from this region. The shape of the dielectric particles was regarded as a sphere, and the particle size (d) was determined by the following equation. Particle size (d) = 2 × (√ (S / π)) × 1.5. The obtained particle diameters were compiled into a histogram, and the value at which the cumulative frequency was 50% was defined as the average particle diameter (D50). The value of D50 is calculated as an average value when n number = 250.

The standard deviation (σ) was calculated according to the following formula. Standard deviation (σ) = √ (((nΣx ² ) − (Σx) ² ) / n (n−1)).

  The ratio p (unit:%) in which the dielectric particles (coarse particles) having an average particle diameter of 2.25 times or more of D50 are present in the entire dielectric particles was also determined from the above observation results.

  4 and 5 show SEM images showing the cross-sectional states of the sintered bodies after thermal etching of Sample 9 and Sample 1, respectively. 6 and 7 are graphs showing the relationship between the particle size and frequency of the dielectric particles constituting the interlayer dielectric layer in Sample 9 and Sample 1, respectively.

  Regarding the measurement of electrical characteristics, the end surface of the obtained sintered body was polished by sand blasting, and then an In—Ga alloy was applied to form a test electrode to obtain a multilayer ceramic chip capacitor sample. The size of the capacitor sample was 3.2 mm long × 1.6 mm wide × 1.0 mm high, the thickness of the interlayer dielectric layer 2 was about 1.1 μm, and the thickness of the internal electrode layer 3 was 0.9 μm. .

  The obtained capacitor sample was evaluated for TC bias, DC breakdown strength, DC bias, and relative dielectric constant ε.

  Regarding the TC bias, the capacitor sample was measured with a digital LCR meter (YHP 4274A) in a constant temperature bath maintained at 85 ° C. with a bias voltage of 120 Hz, 0.5 Vrms, 2 V / μm, and a bias of 20 ° C. The rate of change in capacity from the measured value during no voltage application was calculated and evaluated. The evaluation criteria was good to be greater than −25%.

  The DC breakdown strength is 50 V / sec. The voltage when the leakage current of 0.1 mA was detected (DC breakdown voltage VB, unit: V / μm) was measured, and the average value was calculated. The evaluation standard was 35 V or higher.

  For the DC bias, the capacitor sample was measured with a digital LCR meter (YHP 4274A) at a reference temperature of 20 ° C. under conditions of frequency: 120 Hz, OSC: 0.625 Vrms / μm, bias voltage: 0.5 V / μm. . The evaluation standard was -8% or better.

  The relative dielectric constant ε was measured with respect to a capacitor sample at a reference temperature of 25 ° C. with a digital LCR meter (YHP 4274A) under a frequency of 1 kHz and an input signal level (measurement voltage) of 1.0 Vrms. Calculated from capacitance (no unit). The evaluation standard was 1700 or higher.

The results are shown in Table 1.

As shown in Table 1, in samples 1 to 3 deviating from σ <0.130, the relative dielectric constant ε shows a good value, but all of the TC bias, the DC breakdown voltage VB, and the DC bias are inferior. In particular, as shown in FIG. 5 and FIG. 7, it can be confirmed that Sample 1 has a large variation in the particle size of the dielectric particles and some coarse particles in the interlayer dielectric layer.
On the other hand, in the samples 4 to 9 within the scope of the present invention, it was confirmed that all of TC bias, VB, and DC bias were excellent along with ε. In particular, as shown in FIGS. 4 and 6, in Sample 9, it can be confirmed that there is little variation in the particle size of the dielectric particles and there are almost no coarse particles in the interlayer dielectric layer. Further, it was confirmed from Samples 8 to 9 that even if the value of σ is the same, the effect of improving the TC bias characteristics can be enhanced by reducing p.
In Sample 10, since the firing temperature was low and sintering was insufficient, the evaluation could not be performed. In the sample 11, the sintering shortage can be eliminated by increasing the firing temperature, and it can be confirmed that all of the TC bias, VB, and DC bias are excellent together with ε, similarly to the samples 4 to 9 within the scope of the present invention. It was. Sample 12 could not be evaluated because the sintering was insufficient even at a firing temperature of 1350 ° C.

  It was also confirmed from Table 1 that p tends to increase as σ increases.

Example 2
A capacitor sample was prepared in the same manner as in Example 1 except that the thickness of the interlayer dielectric layer 2 was changed to 1.9 μm, 1.7 μm, 1.5 μm, 1.3 μm, and 0.9 μm. Went. As a result, similar results were obtained.

Comparative Example 1
A capacitor sample was prepared in the same manner as in Example 1 except that the thickness of the interlayer dielectric layer 2 was changed to 2.0 μm and 2.2 μm, and the same evaluation was performed. As a result, when the thickness of the interlayer dielectric layer 2 is 2 μm or more, since the influence of the dielectric material for addition is small, almost no grain growth of the dielectric layer is observed, and ceramic particles in the internal electrode layer (for addition) Almost no difference was observed in the average particle size of the dielectric particles of the interlayer dielectric layer 2 due to the dielectric material).

FIG. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view of a main part of the dielectric layer shown in FIG. FIG. 3 is a graph showing temperature changes in the binder removal processing, firing and annealing in the examples. FIG. 4 is an SEM image showing a cross-sectional state of the sintered body after thermal etching of Sample 9 showing an example. FIG. 5 is an SEM image showing a cross-sectional state of the sintered body after thermal etching of Sample 1 showing a comparative example. FIG. 6 is a graph showing the relationship between the particle size and frequency of the dielectric particles constituting the interlayer dielectric layer in the sample 9 showing the example. FIG. 7 is a graph showing the relationship between the particle size and frequency of dielectric particles constituting the interlayer dielectric layer in Sample 1 showing a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Multilayer ceramic capacitor 10 ... Capacitor element body 2 ... Interlayer dielectric layer 2a ... Dielectric particle 22a ... Contact dielectric particle 24a ... Non-contact dielectric particle 2b ... Grain boundary phase 20 ... Outer dielectric layer 3 ... Internal electrode layer 4 ... External electrode

Claims (2)

A multilayer ceramic capacitor having an internal electrode layer and a dielectric layer having a thickness of less than 2 μm,
The dielectric layer includes a plurality of dielectric particles,
A multilayer ceramic capacitor in which the σ satisfies σ <0.130 when the standard deviation of the particle size distribution of the entire dielectric particles in the dielectric layer is σ (no unit). When the average particle diameter of the entire dielectric particles in the dielectric layer is D50 (unit: μm), the dielectric particles (coarse particles) having an average particle diameter of 2.25 times or more of the D50 2. The multilayer ceramic capacitor according to claim 1, wherein, when the ratio existing in the whole dielectric particle is p (unit:%), the p satisfies p <12%.

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